共查询到20条相似文献，搜索用时 15 毫秒
1.
We propose a new single-phase local upscaling method that uses spatially varying multipoint transmissibility calculations.
The method is demonstrated on two-dimensional Cartesian and adaptive Cartesian grids. For each cell face in the coarse upscaled
grid, we create a local fine grid region surrounding the face on which we solve two generic local flow problems. The multipoint
stencils used to calculate the fluxes across coarse grid cell faces involve the six neighboring pressure values. They are
required to honor the two generic flow problems. The remaining degrees of freedom are used to maximize compactness and to
ensure that the flux approximation is as close as possible to being two-point. The resulting multipoint flux approximations
are spatially varying (a subset of the six neighbors is adaptively chosen) and reduce to two-point expressions in cases without
full-tensor anisotropy. Numerical tests show that the method significantly improves upscaling accuracy as compared to commonly
used local methods and also compares favorably with a local–global upscaling method. 相似文献
2.
The square-root method provides a simple and computationally inexpensive way to generate multidimensional Gaussian random fields. It is applied by factoring the multidimensional covariance operator analytically, then sampling the factorization at discrete points to compute an array of weighted averages that can be convolved with an array of random normal deviates to generate a correlated random field. In many respects this is similar to the LU decomposition method and to the one-dimensional method of moving averages. However it has been assumed that the method of moving averages could not be used in higher dimensions, whereas direct application of the matrix decomposition approach is too expensive to be practical on large grids.
In this paper, I show that it is possible to calculate the square root of many two- and three dimensional covariance operators analytically so that the method of moving averages can be applied directly to the problem of multidimensional simulation. A few numerical examples of nonconditional simulation on a 256×256 grid that show the simplicity of the method are included. The method is fast and can be applied easily to nested and anisotropic variograms. 相似文献
3.
Seismic modeling plays an important role in geophysics and seismology for estimating the response of seismic sources in a given medium. In this work, we present a MATLAB-based package, FDwave3D, for synthetic wavefield and seismogram modeling in 3D anisotropic media. The seismic simulation is carried out using the finite-difference method over the staggered grid, and it is applicable to both active and passive surveys. The code package allows the incorporation of arbitrary source mechanisms and offers spatial derivative operators of accuracy up to tenth-order along with different types of boundary conditions. First, the methodological aspects of finite-difference method are briefly introduced. Then, the code has been tested and verified against the analytical solutions obtained for the homogeneous model. Further, the numerical examples of layered and overthrust models are presented to demonstrate its reliability. 相似文献
4.
A method for interpretation of potential geophysical fields, based on a stable inversion algorithm, is proposed. The stability of the algorithm is provided by an original choice of the zero approximation model and stepwise solution of the inverse problem by a correctness set. The three-dimensional density distribution of local structures as grid functions is reconstructed by layer-wise anomalies of a spilt field. Examples of interpretation of the practical gravimetric data illustrating the efficiency of the method are given. 相似文献
5.
The present study investigates the increasing in ultimate pile capacity and studied the soil plugging phenomenon and the incremental filing ratio for a modified type of open-ended pipe pile. The modification performed by adding steel plates as wings with special dimensions and fixed on the exterior face of the pipe pile wall at a location near the pile tip with specified dimensions. Five wings have used for each new model of pipe pile. These wings distributed in equal spacing along with the circumstances of the exterior wall of the open-ended pipe piles. The efficiency of the proposed type studied by modelling and manufacturing twelve piles (40 mm diameter, L/D = 15 and L/D = 20). Complete setup manufactured for installing and loading the piles in a constant rate of penetration. The model piles installed in poorly graded loose dry sand. The obtained results show that the proposed type has a higher ultimate bearing capacity. The percentage of increase reaches more than 50%. The development of the load capacity is due to the three effects. The first is increases of the exterior shaft friction, and the second effect creates a new end-bearing capacity under the constrained soil between the exterior wings. And the third effect is developing the end-bearing capacity under the soil plug inside open-ended pipe pile due to the first and the second effects. 相似文献
6.
A numerical method for solving an inverse problem of the theory of seismic wave propagation, relying on the modified least square method, is proposed, substantiated, and implemented. The proposed modification is based on the decomposition of the velocity model of the geological medium into the subspaces of smoothly changing propagators and sharply changing reflectors. The modified functional exhibits strong nonlinearity relative to the macro-velocity component, since the operator M, which transforms the time reflector to the space reflector, depends on it significantly. However, the low dimensions of the subspace of the macro-velocity models make it possible to use quite effective minimizing methods successfully. 相似文献
7.
A new low-dimensional parameterization based on principal component analysis (PCA) and convolutional neural networks (CNN) is developed to represent complex geological models. The CNN–PCA method is inspired by recent developments in computer vision using deep learning. CNN–PCA can be viewed as a generalization of an existing optimization-based PCA (O-PCA) method. Both CNN–PCA and O-PCA entail post-processing a PCA model to better honor complex geological features. In CNN–PCA, rather than use a histogram-based regularization as in O-PCA, a new regularization involving a set of metrics for multipoint statistics is introduced. The metrics are based on summary statistics of the nonlinear filter responses of geological models to a pre-trained deep CNN. In addition, in the CNN–PCA formulation presented here, a convolutional neural network is trained as an explicit transform function that can post-process PCA models quickly. CNN–PCA is shown to provide both unconditional and conditional realizations that honor the geological features present in reference SGeMS geostatistical realizations for a binary channelized system. Flow statistics obtained through simulation of random CNN–PCA models closely match results for random SGeMS models for a demanding case in which O-PCA models lead to significant discrepancies. Results for history matching are also presented. In this assessment CNN–PCA is applied with derivative-free optimization, and a subspace randomized maximum likelihood method is used to provide multiple posterior models. Data assimilation and significant uncertainty reduction are achieved for existing wells, and physically reasonable predictions are also obtained for new wells. Finally, the CNN–PCA method is extended to a more complex nonstationary bimodal deltaic fan system, and is shown to provide high-quality realizations for this challenging example. 相似文献
8.
A numerical algorithm for simulation of 2-D (axis-symmetric) wave propagation using a multidomain approach is proposed. The method uses a cylindrical coordinate system, Chebyshev and
Fourier differential operators to calculate the spatial derivatives along the radial and vertical direction, respectively,
and a Runge–Kutta time-integration scheme. The numerical technique is based on the solution of the equations of momentum conservation
combined with the stress–strain relations of the fluid (drilling mud) and isotropic elastic media (drill string and formation).
Wave modes and radiated waves are simulated in the borehole-formation system. The algorithm satisfies the reciprocity condition
and the results agree with an analytical solution and low-frequency simulation of wave-propagation modes reported in the literature.
Examples illustrating the propagation of waves are presented for hard and soft formations. Moreover, the presence of casing,
cement, and formation heterogeneity have been considered. Since the algorithm is based on a direct (grid) method, the geometry
and the properties defining the media at each grid point, can be general, i.e., there are no limitations such as planar interfaces
or uniform (homogeneous) properties for each medium.
相似文献
9.
We propose a methodology, called multilevel local–global (MLLG) upscaling, for generating accurate upscaled models of permeabilities
or transmissibilities for flow simulation on adapted grids in heterogeneous subsurface formations. The method generates an
initial adapted grid based on the given fine-scale reservoir heterogeneity and potential flow paths. It then applies local–global
(LG) upscaling for permeability or transmissibility [ 7], along with adaptivity, in an iterative manner. In each iteration of MLLG, the grid can be adapted where needed to reduce
flow solver and upscaling errors. The adaptivity is controlled with a flow-based indicator. The iterative process is continued
until consistency between the global solve on the adapted grid and the local solves is obtained. While each application of
LG upscaling is also an iterative process, this inner iteration generally takes only one or two iterations to converge. Furthermore,
the number of outer iterations is bounded above, and hence, the computational costs of this approach are low. We design a
new flow-based weighting of transmissibility values in LG upscaling that significantly improves the accuracy of LG and MLLG
over traditional local transmissibility calculations. For highly heterogeneous (e.g., channelized) systems, the integration
of grid adaptivity and LG upscaling is shown to consistently provide more accurate coarse-scale models for global flow, relative
to reference fine-scale results, than do existing upscaling techniques applied to uniform grids of similar densities. Another
attractive property of the integration of upscaling and adaptivity is that process dependency is strongly reduced, that is,
the approach computes accurate global flow results also for flows driven by boundary conditions different from the generic
boundary conditions used to compute the upscaled parameters. The method is demonstrated on Cartesian cell-based anisotropic
refinement (CCAR) grids, but it can be applied to other adaptation strategies for structured grids and extended to unstructured
grids. 相似文献
10.
在位场数据处理中,垂向导数具有重要的物理意义。其在一定程度上可以划分不同深度和大小异常源产生的叠加异常,且导数的阶次越高,这种分辨能力就越强,但通常认为高阶导数的换算是不稳定的。本文在Tikhonov正则化求位场垂向高阶导数的基础上,结合迭代法进行逐次逼近,提出了位场高阶导数的Tikhonov正则化迭代法,并且得到Tikhonov正则化迭代法的递推公式。通过对该方法的滤波特性分析可以看出,该方法计算的位场垂向高阶导数具有一定的稳定性及保幅性。模型试验和实际数据的处理表明,该方法计算结果较常规FFT求导法有更高的稳定性和实用价值。 相似文献
11.
As the scale of the power grid becomes larger, the requirements for transmission reliability are getting higher. Due to the large geographical span and the harsh environment of the power transmission line, it has become the most severely affected equipment of the power grid by natural factors. However, the quantitative assessment of transmission line tripping accidents caused by multiple natural hazards has rarely been investigated. In this study, a risk analysis method to probabilistically analyze the tripping accidents of power transmission lines caused by wildfire, lightning, strong wind and ice storm was proposed. The analysis process consists of comprehensively identifying the risk of tripping accidents based on fault tree analysis and dynamically performing the predictive analysis of tripping accident evolution process in transmission line from causes to consequences based on Bayesian network. Critical risk evolution paths corresponding to four natural hazards are determined through a 72-node BN. The source risks of the four critical risk evolution paths are artificial ignition source from the wildfire path, aging from the lightning path, thoughtless of surrounding environment from the strong wind path and wind effect from the ice storm path. The countermeasures of tripping accidents are derived through the source risks and synergy between risks in three scenario analysis. This study is expected to examine the key challenges of risk management in power grid tripping accidents, which provides technical supports for accident preventing, handling and recovering of tripping accidents of the power transmission line according to “scenario–response”-based hazard response strategy. 相似文献
12.
In many spatial interpolation fields, high accuracy surface modeling (HASM) has yielded better accuracy than classical interpolation methods. The Gaussian equation is the core of the HASM algorithm; The current version of the HASM method builds the Gaussian equation in Cartesian coordinates and, computes the two partial derivatives of the surface in the horizontal and vertical directions for each grid. In this paper, a modified HASM method is proposed that integrates flow paths to improve the original HASM methodology. The modified HASM approach involves two steps. The first step generates an initial DEM, which is used to compute the flow path. Then, the second step is conducted based on scatter points and the flow direction. The output from this step is better than the initial DEM. First, we used a theoretical mathematical surface to validate the correctness of the modified model. Then, we chose a small study area where the topography is affected by hydrological erosion for analysis. The test results showed that the modified HASM method constructed a DEM with low MAE and RMSE values compared to those of traditional methods, and it more accurately characterized topographic features. Finally, a relatively gently sloping area was selected to validate that the applicability of the new method in other areas. 相似文献
13.
通过分析地基沉降预测模型,指出最小二乘的病态性会导致模型参数求解失败。应用正则化理论,基于矩阵求逆理论,提出了一种沉降预测模型参数的正则化无偏估计算法,说明了新算法的无偏性和方差最小性。在一定条件下,证明了新算法中正则参数的存在性,并给出了正则参数的计算公式。结合文献和工程实例进行的分析表明,新算法降低了矩阵条件数,减轻矩阵病态程度,能有效求得地基沉降预测模型参数。 相似文献
14.
Hesitant fuzzy set is an extension of the traditional fuzzy set, and it has the membership function which was expressed by several possible numbers. Since it was introduced, it has been received wide attention from scholars due to its powerful ability in describing the uncertainty. In this paper, we first introduce some new operations on hesitant fuzzy elements (HFEs) based on Dombi t-conorm and t-norm and then proposed some new aggregation operators for HFEs, such as hesitant fuzzy Dombi weighted averaging, hesitant fuzzy Dombi ordered weighted averaging, hesitant fuzzy Dombi weighted geometric, hesitant fuzzy Dombi ordered weighted geometric, hesitant fuzzy Dombi hybrid averaging and hesitant fuzzy Dombi hybrid geometric operator. Finally, a multiple attribute group decision-making approach under hesitant fuzzy environment is presented based on these proposed operators. A real example about typhoon disaster assessment is presented to show the advantages of the proposed method. 相似文献
15.
A procedure for the improved calculation of upscaled grid block permeability tensors on Cartesian grids is described and applied. The method entails the use of a border region of fine-scale cells surrounding the coarse block for which the upscaled permeability is to be computed. The implementation allows for the use of full-tensor permeability fields on the fine and coarse scales. Either periodic or pressure–no flow boundary conditions are imposed over the extended local domain (target block plus border regions) though averaged quantities, used to compute the upscaled permeability tensor, are computed only over the target block region. Flow and transport results using this procedure are compared to those from standard methods for different types of geological and simulation models. Improvement using the new approach is consistently observed for the cases considered, though the degree of improvement varies for different models and flow quantities. 相似文献
16.
Zusammenfassung Die Wahl des Zählpunktabstandes für die Auszählung von Gefügediagrammen auf dem Schmidtschen Netz wird diskutiert. Es wird gezeigt, daß bei Verwendung eines Zählpunktabstandes von 0.5 cm die Schwerpunkte der Maxima der Polverteilung mit genügender Genauigkeit erfaßt werden. Als Zählfläche wird der Kreis von 1% der Netzfläche gewählt. Verwendung von Zählkreisen verschiedener Größe in einem Diagramm führt zu falschen Ergebnissen. Es wird eine Norm für das Auszählen vorgeschlagen, um Gefügediagramme reproduzierbar zu machen.Für die Darstellung des Regelungsgrades wird eine Methode vorgeschlagen, die vom Gefügediagramm ausgeht, aber auf der tatsächlichen Polverteilung fußt und ohne große Rechenoperationen auskommt. Durch diese Methode lassen sich gleichartige Gefügediagramme verschiedener Polzahl miteinander vergleichen.
Summary The grid size for counting fabric diagrams on the Schmidt net is discussed. It can be shown that counting out at each corner of a 0.5 cm square grid will grant sufficient accuracy in indicating the location of each maximum of the diagram. A circle of 1% of the Schmidt net's area is chosen to act as counting circle. Inaccuracies will occur if counting circles with different areas are used for counting the same fabric diagram. A rule for counting fabric diagrams is proposed in order to make the diagrams reproduceable.A method is proposed for computation of the degree of orientation. This method uses the counted and contoured fabric diagram, but it is based on the real distribution of the points, and no great computations are involved. This method allows fabric diagrams derived from different numbers of poles to be compared.
Mit 17 Textabbildungen
Nach einem Vortrag, gehalten am 11. Mai 1964 vor der Österreichischen Mineralogischen Gesellschaft in Wien. 相似文献
17.
Regional agricultural drought vulnerability (RADV) is a complex problem caused by the interaction of various factors, and the combination of multiple dimensions of each subregion, factor index and time affects the RADV. Therefore, panel data should be used to reflect the actual situation of the region objectively and comprehensively. Current research on identifying key factors of affecting RADV is relatively scarce from the perspective of panel data. In view of this, in order to classify and identify the key factors, a new panel data grey combined method of comprehensive grey relational analysis (CGRA) and Max-CGRA clustering is proposed, which is applied to identify the key factors of RADV in China’s Henan Province. According to the identification results of key factors, the reasons for the change of RADV are further discovered, and the corresponding drought policies and countermeasures that need to be strengthened and controlled are presented. In addition, these results can also provide scientific basis for regional agricultural drought risk control. 相似文献
18.
Wells are seldom modeled explicitly in large scale finite difference reservoir simulations. Instead, the well is coupled to the reservoir through the use of a well index, which relates wellbore flow rate and pressure to grid block quantities. The use of an accurate well index is essential for the detailed modeling of nonconventional wells; i.e., wells with an arbitrary trajectory or multiple branches. The determination of a well index for such problems is complicated, particularly when the simulation grid is irregular or unstructured. In this work, a general framework for the calculation of accurate well indices for general nonconventional wells on arbitrary grids is presented and applied. The method entails the use of an accurate semianalytical well model based on Green's functions as a reference single phase flow solution. This result is coupled with a finite difference calculation to provide an accurate well index for each grid block containing a well segment. The method is demonstrated on a number of homogeneous example cases involving deviated, horizontal and multilateral wells oriented skew to the grid. Both Cartesian and globally unstructured multiblock grids are considered. In all these cases, the method is shown to provide results that are considerably more accurate compared to results using standard procedures. The method is also applied to heterogeneous problems involving horizontal wells, where it is shown to be capable of approximating the effects of subgrid heterogeneity in coarse finite difference models. 相似文献
19.
We consider a system of nonlinear partial differential equations that arises in the modeling of two-phase flows in a porous medium. The phase velocities are modeled using a Brinkman regularization of the classical Darcy’s law. We propose a notion of weak solution for these equations and prove existence of these solutions. An efficient finite difference scheme is proposed and is shown to converge to the weak solutions of this system. The Darcy limit of the Brinkman regularization is studied numerically using the convergent finite difference scheme in two space dimensions as well as using both analytical and numerical tools in one space dimension. The results suggest that the Brinkman regularization may not approximate the accepted entropy solutions of the Darcy model and raise fundamental questions about the use of Brinkman type models in two-phase flows. 相似文献
20.
针对点质量核径向基函数应用于局部重力场建模中的设计矩阵严重病态问题,本文引入Tikhonov正则化方法对传统点质量核径向基函数方程进行改造,建立了相应的正则化模型。通过模拟数据进行仿真实验,以传统格网化方法作为对比试验,利用"标靶法"确定两种模型的最优结构。实验结果表明:正则化点质量核径向基函数可以直接利用离散数据进行局部重力场建模。在两种模型的最优结构下,当实测数据无污染时,正则化方法达到与传统格网化方法相当的精度;当实测值中加入3 mGal的高斯白噪声时,正则化方法的精度获得了27.9%的提升。这说明本文方法可以应用于局部重力场建模中,且模型结构更优,抗干扰能力更强。 相似文献
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